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Background: The hamstring injury mechanism was assessed by investigating the exercise-related metabolic activity characteristics of the hamstring muscles using a muscle functional MRI (mfMRI) protocol., Methods: 27 healthy male football players and 27 football players with a history of hamstring injuries (recovered and playing fully) underwent standardised mfMR Imaging. The mfMRI protocol consisted of a resting scan, a strenuous bilateral eccentric hamstring exercise and a postexercise scan. The exercise-related T2 increase or the signal intensity shift between both scans was used to detect differences in metabolic activation characteristics (1) between the different hamstring muscle bellies and (2) between the injury group and the control group., Results: A more symmetrical muscle recruitment pattern corresponding to a less economic hamstring muscle activation was demonstrated in the formerly injured group (p<0.05). The injured group also demonstrated a significantly lower strength endurance capacity during the eccentric hamstring exercise., Conclusions: These findings suggest that the vulnerability of the hamstring muscles to football-related injury is related to the complexity and close coherence in the synergistic muscle recruitment of the biceps femoris and the semitendinosus. Discrete differences in neuromuscular coordination and activity distribution, with the biceps femoris partly having to compensate for the lack of endurance capacity of the semitendinosus, probably increase the hamstring injury risk., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)